The objective of this study is to isolate viral specific proteins from (1) avian cells, including chick and duck embryo cells infected with viruses of the avian leukosis and sarcoma complex as well as uninfected chick helper factor positive chick embryo cells, and (2) mammalian cells including rat cell lines infected with temperature sensitive mutants of avian sarcoma viruses. In general we propose to label cell proteins and glycoproteins endogenously with radioactive amino acids and carbohydrate and exogenously by means of lactoperoxidase catalysed iodination. Labeled viral specific proteins, including viral structural proteins and the tumor specific surface antigen, will be isolated from intracellular lysates by use of specific antisera and characterized on polyacrylamide gels. The quantitation and characterization of these proteins should aid in understanding the mechanism of viral replication and cell transformation.